The present invention relates to an exposure method to be used in manufacturing semiconductor devices or liquid crystal displays and an exposure apparatus for carrying out the method.
Proximity exposure methods are used to transfer a mask pattern of a mask to photosensitive agent applied to a surface of a glass substrate (hereinafter referred to as substrate) or a wafer held in proximity to the mask by irradiating the mask by a light beam emitted by a light source positioned above the mask. Comparing the proximity exposure methods with projection exposure methods, the former can be carried out at a lower cost than the latter because the former do not require a complicated lens system or a stage which can be operated with high accuracy. Further, unlike contact exposure methods, the mask does not contact the substrate in the proximity exposure methods. Thus, the photosensitive agent can be prevented from being damaged or torn off from the substrate, and hence, failure does not occur. In the proximity exposure methods, the resolution of an image formed by transfer depends greatly on the gap between the mask and the substrate.
Supposing that the wavelength of a light beam emitted by a light source is X and the gap between the mask and the substrate is (g), a minimum line width (ds) of the image formed by transfer is expressed as follows: ##EQU1##
In order to resolve a line having a width of approximately 3 .mu.m by using a mercury lamp as a light source, it is necessary to adjust the gap between the mask and the substrate to as close as approximately 10 .mu.m. Generally, the substrate is wavy in an extent of approximately 10 .mu.m through 20 .mu.m. Thus, it is necessary to adjust the gap between the mask and the substrate very precisely in consideration of this waviness. To this end, a complicated construction is required. A method of using a substrate-flattening chuck for keeping the upper surface of the substrate flat by deforming it is known as disclosed in Japanese Laid-Open Patent Publication No. 59-17247.
An example of a conventional proximity exposure method and a conventional apparatus for carrying out the proximity exposure method are described below with reference to FIG. 20.
In the conventional proximity exposure apparatus essentially, there are provided an exposure station 115 and a height-measuring station 116. In detail, the apparatus comprises a guide rail 112 constituting the base of the apparatus; a mask height-measuring device 114 installed on the guide rail 112 and movable in an X-direction along the guide rail 112 in sliding contact therewith; an X-stage 111 installed on the guide rail 112 and movable in the X-direction along the guide rail 112 in sliding contact therewith; a Z-stage 110 connected with the X-stage 111; a flattening chuck 109 installed on the Z-stage 110; a plurality of vertically movable elements 118 provided inside the flattening chuck 109; a substrate 20 sucked to and held by the flattening chuck 109; a mask 21 held in proximity to the substrate 20; a mask chuck 18 for sucking the mask 20 thereto and holding it thereon; an alignment scope 19 fixed to an upper portion positioned above the mask 21; a substrate height-measuring device 113 installed at a position opposed to the substrate 20; a mercury lamp 11; a reflection mirror 12; a fly eye lens 103; a condensing lens 104; a substrate stage 117 composed of the flattening chuck 109, the Z-stage 110, and the X-stage 111.
The operation of the conventional proximity exposure apparatus having the above-described construction is described below.
The substrate stage 117 on which the substrate 20 has been placed is moved to the height-measuring station 116 along the guide rail 112. Then, the substrate height-measuring device 113 installed above the substrate 20 measures the height of the upper face of the substrate 20. The mask height-measuring device 114 moves to the exposure station 115 along the guide rail 112, thus measuring the height of the lower face of a mask 21. Based on the measured values, the level of the vertically movable elements 118 provided inside the flattening chuck 109 and that of the Z-stage 110 are adjusted so as to set a gap between the mask 21 and the substrate 20 at respective measured positions to a desired value. Then, the substrate stage 117 is moved to the exposure station 115, and the substrate 20 and the mask 21 are placed in position by using the alignment scope 19. A light beam emitted by the mercury lamp 11 is reflected by the reflection mirror 12 to guide it to the fly eye lens 103 to make the diameter thereof uniform. Then, the light beam is adjusted to be parallel to expose the photosensitive layer formed on the substrate 20 to a light beam through the mask 21 supported by the mask holder 18.
The above-described conventional proximity exposure apparatus having the construction is an exposure type apparatus in which a substrate is exposed to a light beam through a mask by one exposure operation. Thus, it is difficult to compensate the magnification of the mask pattern. In addition, it is necessary to provide the apparatus with the height-measuring station 116 separately from the exposure station 115. Thus, the apparatus is large. Moreover, if the large substrate 20 is used, it is necessary to use the condensing lens having a large diameter. Hence, the apparatus is manufactured at a high cost. Further, the mechanical accuracy of the guide rail is important for accurately measuring the gap between the substrate 20 and the mask 21.